Re: [Boost-users] Questions about packaged_task , Promise and serialization of a class object and event handling

Subject: Re: [Boost-users] Questions about packaged_task , Promise and serialization of a class object and event handling
From: Vicente J. Botet Escriba (vicente.botet_at_[hidden])
Date: 2012-04-15 13:57:49

Le 15/04/12 18:57, Master a écrit :
> Hello all again .
> i have couple of questions again which i would appreciate any kind of 
> help and answer,
> my first question is about packaged_task and how we can use it ,
> i mean i tried using packaged_task with functions ,  with parameters , 
> and i got errors doing it . so do we always have to use class or 
> stcucts in order for us to use packaged_task ?
Hi,
The current implementation of packaged_task are nullary, no arguments 
are allowed.

template<typename  R>
class  packaged_task {
     // execution
     void  operator()();
}

Waiting for

template<class R, class... ArgTypes>
class packaged_task<R(ArgTypes...)> {
   void operator()(ArgTypes... );
}

you will need to use a functor.

> how can i send some arguments to a function when im trying to make a 
> package out of ?
Have you tried boost::bind?
>
> can someone show me a simple sample of using Promise in threading ? i 
> mean i already know about future , whats the need for Promise ? !
>
Promise is the on of the basic class of the Boost.Thread/Futures design. 
In order to have a future you need a promise, a way to provide a value. 
packaged_task encapsulates a function with a promise and a future. When 
the functions ends the result is set on the promise so that you could 
retrieve it using the associated future.

Bat see 
http://www.justsoftwaresolutions.co.uk/threading/multithreading-in-c++0x-part-8-futures-and-promises.html 
for an example.
for  better explanation and a concrete example.

Best,
Vicente